An improved method to determine the molecular weight of alcohol dehydrogenase after sodium dodecylsulfate polyacrylamide gel electrophoresis(SDS-PAGE) has been developed. This method was based on the finding that on a gel, which was washed with a buffer to remove SDS after SDS-PAGE, stained with an enzymatic activity staining mixture and then stained with coomassie blue, there appeared two active stained bands with apparent molecular weights of 148,000(tetramer)and 35,000(monomer)on the SDS-PAGE gel. The method developed here may be applicable to a wide range of active stainable-enzymes as a rapid and simple molecular weight determination method after SDS-PAGE.